1. Field of the Invention
This invention pertains to an improved process for the removal of acid gases, such as CO.sub.2 and H.sub.2 S, from gas mixtures. More specifically, the present invention significantly decreases the consumption of heat needed for regenerating the rich alkaline scrubbing solution which is used to remove the acid gases from the gas mixtures.
2. Discussion of Related Art
The industrial importance of gas scrubbing processes involving the bulk removal of acid gases, particularly CO.sub.2 and H.sub.2 S, from various raw gas mixtures is steadily increasing. As the demand for synthetic fuels and synthesis gases derived from fuel sources such as natural gas, oil and coal increases, there is an ever-increasing need for efficient processes for the removal of acid gases from the raw gas mixtures that are generated. For example, in the production of synthetic methane from naphtha, fuel oil or coal, the starting material is subjected to reforming or partial oxidation, producing a raw gas containing, e.g., from 20% to as much as 50% of CO.sub.2 together with smaller amounts of H.sub.2 S where a sulfur-containing starting material is employed. Similarly, in the reforming of natural gas to produce hydrogen for ammonia synthesis or hydrogenation reactions, a raw gas is produced containing usually from 16% to 20% CO.sub.2, all of which must be removed prior to the ammonia synthesis step.
A typical system for removing the acid gases from the gas mixtures, as described in, for example, U.S. Pat. Nos. 3,823,222 and 4,160,810, consists of an absorber in which the feed gas containing the acid gas components is scrubbed countercurrently at elevated pressure with an alkaline scrubbing solution. The resulting rich solution containing the scrubbed acid gases is then regenerated by first flashing a minor part of the absorbed acid gases as the rich solution enters the vapor head of a steam stripping column where it is then boiled and steam stripped to form a lean solution capable of being recycled back to the absorber.
In an alternate process, such as described in U.S. Pat. Nos. 4,537,753 and 4,551,158, for example, the steam stripping column of the above process is eliminated and the rich scrubbing solution is regenerated simply by flashing in one or more flash stages.
In U.S. Pat. No. 3,622,267, rich scrubbing solution is flashed and then passed through a steam stripping column. The overhead vapor stream from the steam stripping column containing removed acid gases and steam is introduced into the flashing means and is utilized as an additional stripping medium therein.
However, a need still exists to develop an even more efficient and economical process for the removal of the acid gases by means of a scrubbing solution and the subsequent regeneration of the acid gas-laden scrubbing solution.